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    <title>Document</title>
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<body>

    <script>

        // 闰年
        //   普通闰年：能被4整除，且不能被100整除
        //   世纪闰年：能被400整除


      

        var year = Math.round(Math.random() * (3000 - 1000)) + 1000 ;
        if(year % 400 === 0 || year % 4 === 0 && year % 100 !== 0) {
            alert(year + '是闰年')
        }
        else {
            alert(year + '品年')
        }


        var a = 1 ;
        var b = a++ * 2 ;
        console.log(b) ;
    </script>
    
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